Animal agriculture has recently received much attention,1, 2 for its role in producing gases that contribute to global climate change. Prominent among those gases so produced is methane, which cattle emit as a consequence of their digestion.

Based on the estimate that the typical grass-fed cow produces 600–700 liters of methane per day,3 we can calculate the amount of this gas annually produced by cattle that graze on 260 million acres of federal public lands managed by the U.S. Forest Service and the Bureau of Land Management in the forty-eight contiguous states.4 In the interest of producing a conservative estimate, I will perform the calculation using the lower limit (i.e., 600 liters) of a cow’s daily methane production.

The BLM5 and U.S. Forest Service6 report annual forage utilization from their lands by cattle of 7,862,879 and 6,025,788 AUMs7 respectively, with the combined forage utilization being 13,888,667 AUMs.

As each AUM represents thirty-one days of a cow’s forage consumption, it likewise represents thirty-one days of a cow’s methane production. In other words, each AUM consumed produces (31 days × 600 liters/day) of methane. Or performing the calculation: 18,600 liters of methane.

Consequently, the annual volume of methane produced by public lands cattle is equal to (18,600 liters/AUM) x (13,888,667 AUMs/year), or 258,329,206,200 liters.